Apertured electrode for thermionic tubes



Jan. 2,1949.. H, s BAMFORD 2,185,395

HARRY S. EMFORD.

W ATToRNEYs.

A in sharp contrast the anode aperture 5, by means of which signals froman input lead 9 may be utilized to control the intensity of the beampassing through the anode aperture.

The cathode is energized by cathode heating w battery lO and anaccelerating potential is placed upon anode 4 by anode source ll. Incase additional acceleration 'is desired an'auxliary acceleratingelectrode may be used, and I prefer to position this electrode betweenanode 4 and the fluorescent screen 1. This accelerating electrodeembodies my present invention and comprises an electrode support ring|2, across which ist stretched a kntted fabric id. The fabric ismaintained in position, preferably by splitting support l2, placing thefabric across one half of the ring, placing the other half over thefabric, and welding both halves to fix the fabric between the two halfrings. The fabric M is lmitted, and I have found that the fabric may beknitted on standard knitting machines, such as, for example, thoseutilized to make silk stockings, and the Wire utilized for theaccelerating fabric may be, for example, molybdenum, tantalum, tungsten,nickel, or any ductile metal of lower melting points, in case theaccelerating electrode is not subjected to heavy bombardments.

Inasmuch as the aceelerating electrode here is used only for theproduction of an accelerating field, it is obvious that within certainlimits.

the mesh aperture should be large in proportion to the wire diameter; inother words, here it is desirecl that the large majority of theelectrons shall pass through the electrode, and as few as possibleintercepted thereby. This is, of course, to the two above-mentionedpatents, where it was desired to intercept vas many (electrons aspossible in order to produce bombardment of the fabric. I thereforeutilize very fine wire for the fabric and make the meshes `relativelylarge, and I have found that it is possible to make a satisfactoryaccelerating electrode fabric where the ratio of Wire diameter to mesh'aperture diameter is to 1.

After the accelerating electrode has been mounted in the desiredposition, an exterior lead |5 is provided so that the electrode may begiven an' accelerating potential from auxiliary source IS. 'Ijhe tube isthen exhausted, and when placed in operation the beam from anode 4 maybe deflected over the screen in a pattern as predetermined by the actionon the beam of scanning oscillatorsv ll and IB, energizing magneticdeflection coils .|9 and 20, respeotively.

It will thus be seen that the accelerating electrode l4 is subject todifferential heating which, if not compensated for, will tend to buckleor displace the fabric out of its normal plane, therebychanging theelectrostatic field set up by it and distorting the image produced onthe screen 1. The loops of the knitted fabric, however, quickly absorbthe expansion and contraction of the wires due to the passage thereoverof the beam, and prevent any substantial distortion from the normalplane of the fabric as a whole. I have thus been able to utlize, withoutwelding at cross-overs, a fabric screen electrode having exceptionallyfine wire slzes, without breaking and without any substantial deviationfrom the normal plane.

In the example given above, the differential heating of the screenoccurs by reason of the passage thereover of a moving electron beam.

In the example shown in Figure 2, however, the

differential heating is caused by an entirely different factor. Here Ihave shown, in its very simplest form, a photoelectric tube comprising acathode and an anode 2|. case comprises a support |2, exactly similar tothat previously described, and a knitted fabric |4 supported thereby inexactly the same manner as previously described, except that in thiscase I prefer to form the wires of the fabric from silver and to makethe wire-to-aperture-size ratio between l to 5 and l to '100, dependingupon circumstances, and I have found that there is no difficulty inknitting fine silver Wire to the smallei' mesh. The silver cathode, inthis case,`is supported on a stem 22, the anode 2| is supported from thewall by lead 23, and the difference of potential is placed between thecathode and anode by source 24 Operating through output device 25, whichmay well be a work circuit. After the silver fabric has been mounted inposition it may then be oxidized and sensitized from a source of caesiumor other material 26 having a low work function, as is well known intheV art.

The cathode in this' If, then, an image from light source 21 is l thrownon the silver screen 14 through a lens 28, different parts of the silverscreen will be illumnated to a greater or lesser degree and, inconsequence, heated to a greater or lesser degree; and if the knittedfabric is utilized here the entire cathode Will maintain its normalplane in spite of its differential heating, and thus the field betweenthe anode and cathode will not become distorted. Electrons emitted onthe front surface of the fabric |4 will be pulled through the aperturesby the accelerating potential and over to anode 2|, and if it isdesired, a focusing coil or other focusing device may be utilizedbetween anode and cathode to maintain the electrons in parallelrelationship so that an electron image may be formed which can beutilized in any desired manner, although my cathode screen in this caseis not by any means limited to use in forming such an electron image.

I have therefore provided and given two instances of electrodes Within athermionic tube envelope which are subjected to differential heating,and vwhich will, if made of knitted fabric, maintain their normal planesunder such differential heating without the necessity of weldingcross-overs, thus allowing an extremely fine Wire to be utilized inmaking the fabric. I have thus been able to greatly reduce the area ofthe electrode as far as Wire size is concerned, and have provided anexceptionally strong screen and one which cannot be warped or distortedin use, thereby preventing field distortions when energized.

I claim:

1. An electrical discharge tube having an envelope containing anelectrode comprising a fabric of refractory wire, said fabric having asingle Wire formed into a single chain of loops through which anotherrow of loops of said wire is passed `to produce a Warp knit fabric, anda cooperating electrode.

2. An electron discharge tube having an envvelope' containing anelectrode comprising a

